(1) Field of the Invention
The present invention relates to a rotary cutting tool for use in drilling and end milling workpieces, more particularly to a rotary cutting tool with an efficient cutting edge at the center of rotation of the facing end thereof and with substantially balanced bending moments around the tool axis.
(2) Description of the Prior Art
In conventional drills, there is a problem of poor cutting quality at the chisel edge of the drill point. Due to this, an excessive axial thrust pressure is required for machining work. Various proposals have been made up until now to overcome this problem.
One such proposal has been for provision of a cemented carbide-tipped drill with a straight cutting edge extending from the center of the drill point to or close to the periphery on one side and a straight cutting edge extending from a noncutting edge in the central area to or close to the periphery on the diametrically opposite side.
In such a drill, however, only part of the bending moments occurring around the drill axis due to cutting resistance along the two cutting edge lines can be counterbalanced. As a result, there is a tendency to flexure of the drill. This creates problems as to accuracy of the size and straightness of the drilled holes, which is particularly disadvantageous when drilling deep holes.